This invention relates to a method and apparatus for extraction of underground pipe by a technique which involves pulling a portion of the pipe into an opening formed in the ground at one end of the portion without the necessity for excavating along the full length of the pipe portion.
The replacement of existing underground pipe is becoming more important now that the pipes are becoming old with the danger of breakage and leaking. It is well known that in many situations it is highly desirable to be able to remove the pipe without the necessity for excavating along the full length of the pipe particularly where the pipe crosses busy highways, rail lines or other obstacles. However the desirability of carrying out this step is known, up till now no suitable apparatus or method has been available to enable this to be carried out. This is particularly because the amount of force involved in pulling a significant length of the pipe from the ground is extremely high and no practical technique for generating this significant level of force has up till now been available.
Less satisfactory techniques have therefore involved pulling a wedge along the pipe which forces the pipe outwardly breaking it into pieces which is then forced radially outwardly into the ground surrounding the position of the original pipe. A replacement pipe can then be pulled longitudinally through the opening thus formed. This technique involves significantly less force and is thus readily available but is in many cases impractical since the broken pieces of the pipe generally of cast iron or steel are very sharp and can then penetrate the replacement pipe as the ground resettles.
Another technique shown in U.S. Pat. No. 4,626,134 (Coumont) attempts to pull the pipe by a hydraulic ram arrangement which is inserted into the pipe from one end and then acts to grasp an end of a pipe section and pull it into the opening where the ram is located. This device has achieved little success in view of the fact that it is highly inefficient to pull the pipe one section at a time and in view of the fact that the hydraulic ram in many cases cannot generate enough force to provide the pulling action. The technique is also limited to relatively small pipes.